I like to consider just listing as many alternatives as I could manage, in order of decreasing likelihood (as per my personal estimation): 1) Some kind of psy-

I like to consider just listing as many alternatives as I could manage, in order of decreasing likelihood (as per my personal estimation): 1) Some kind of psy-ops from within our own government, meant to mess with a different government or a branch of our own government. Maybe its own citizens. You can get eleven-dimensional chess with this pretty quickly. 2) We have grabbed someone else's UAVs. Maybe China, maybe Russia. 3) We have grabbed the UAVs of an unsuspected party which a surprise technological edge we would never expect: the Wakanda Hypothesis. We don't even know that we're in a game and that we're losing. ... N-3) Aliens have emerged from local gas giants and are curious about us. Jupiter? Saturn? Neptune? And so on. Probably not Pluto. N-2) Generation ships or "sleepers" from another solar system are on some sort of grand tour of the Orion Arm, working their way out. We've been noticed and the occupants awakened. Aliens? AI? Maybe there is no difference by then. N-1) Aliens within a light sphere about 0.45 * (First UFO Year - 1895) heard our radio and really hustled to get here with a hefty blueshift. N) The captured vessels are either FTL-capable or brought here on a larger ship with such capabilities. All bets are off. There is another possibility which I think is often ignored, after #3. It's sci-fi, but it isn't physics-breaking the way FTL is. What if the craft are from a parallel earth? I dislike it, but not as much as I dislike FTL. It doesn't even require aliens. A parallel history where we got the ball rolling even a few decades earlier might end up with a civilization a hundred or a thousand years ahead of ours. I wouldn't bet money on anything higher than #2 on my list, but I still think that if we are going to conjecture about aliens, we might as well do parallel Earths, too.